Manufacturing method of mounting structure, and sheet therefor

A manufacturing method of a mounting structure, the method comprising:

• a step of preparing a mounting member including a first circuit member and a plurality of second circuit members placed on the first circuit member;
• a disposing step of disposing a thermosetting sheet and a thermoplastic sheet on the mounting member, with the thermosetting sheet interposed between the thermoplastic sheet and the first circuit member;
• a first sealing step of pressing a stack of the thermosetting sheet and the thermoplastic sheet against the first circuit member, and heating the stack, to seal the second circuit members and to cure the thermosetting sheet into a cured layer;
• and
• a removal step of removing the thermoplastic sheet from the cured layer, wherein
• at least one of the plurality of the second circuit members is a hollow member having a space from the first circuit member, and
• in the first sealing step, the stacked sheets deform along with plastic deformation of the thermoplastic sheet so as to conform to contours of gaps between the second circuit members, and the plurality of the second circuit members are sealed so as to maintain the space,
• a thermosetting material constituting the thermosetting sheet exhibits a loss tangent tan δ of 0.1 or more and 0.8 or less, and a storage shear modulus of 1×104 Pa or more and 1×107 Pa or less, at a temperature t when the second circuit members are sealed, and
• a thermoplastic material constituting the thermoplastic sheet exhibits a loss tangent tan δ of 1.5 or less at the temperature t.